This invention relates to methods of preventing the polymerization of acrylic acid and acrylate derivatives, and to acrylic acid and acrylate derivatives comprising a small amount of a polymerization inhibitor.
The prior art discloses that any number of derivatives of 2,4-pentanedione can be used for the production of acrylic acid and its functional derivatives (see, for example, U.S. Pat. Nos. 2,845,451 and 2,886,591). In addition, U.S. Pat. No. 3,627,820 discloses a process for polymerizing acrylic acid and acrylate monomers in the presence of a catalyst consisting of a complex compound of 2,4-pentanedione with trivalent manganese and a mercaptan.
On the other hand, polymerization inhibitors for acrylic acid, acrylates and their derivatives are well known but these inhibitors that are used commercially generally have very low vapor pressures. Although such polymerization inhibitors provide satisfactory results for the storage of acrylic acid, acrylates and their derivatives under normal conditions, they suffer from certain disadvantages. For example, when the monomers are vaporized and condensed on a cooling surface, especially those surfaces that will catalyze the polymerization of acrylates, acrylic acid and their derivatives, these monomers will polymerize and form undesirable deposits on equipment, storage vessels and the like.
These and other disadvantages in the prior art are overcome by the present invention, which provides a polymerization inhibitor for monomers of acrylic acid, acrylates and derivatives thereof, which has a vapor pressure similar to that of these monomers and, thus, will prevent polymerization on surfaces where the monomers may condense. Such a polymerization inhibitor is particularly desirable when acrylic acid, acrylates and derivatives thereof are vaporized, as for example, during the course of a distillation, and thereafter condensed to separate these monomers from other components in a mixture.